The present invention relates to a platform monitoring system which permits an operator or the like on the vehicle side such as a vehicle running on a track to monitor a situation on a platform (how passengers are getting on and off a train, and so on).
When a train stopping at a platform is to leave the platform, it is necessary to confirm the safety as to whether or not any passenger is being caught by a door of the train, and so on before the train is started. Not only that, a continuous safety check is requested in some cases as to whether or not any passenger caught by a door is being dragged in a predetermined range of running immediately after the start as well to duplicate the safety check such that neglected safety check before the start will never result in a grave accident.
While a crew has visually confirmed the safety as mentioned in the past, a platform monitoring system has been provided for permitting an operator or the like to monitor a situation on a platform as so-called one-man operated trains, without crews, have been increasingly introduced.
An example of a conventional platform monitoring system will be described with reference to FIG. 5. FIG. 5 is a schematic plan view generally illustrating an exemplary configuration of some components of a conventional platform monitoring system. In FIG. 5, reference numeral 1 designates a track; 2, a vehicle (a train in the illustrated example) running on the track 1; 3, a platform; and an arrow X, a direction in which the vehicle 2 runs.
The conventional platform monitoring system illustrated in FIG. 5 comprises television cameras 4a-4c installed on the ground side for capturing situations on the platform 3; an optical wireless transmission system for transmitting images captured by the television cameras 4a-4c to the vehicle side as optical signals; and a television monitor (not shown) installed near an operator""s seat in the vehicle 2 for displaying images transmitted by the optical wireless transmission system. The optical wireless transmission system comprises an optical transmitter installed on the ground side, and an optical receiver installed on the side of the vehicle 2. The optical transmitter has a multiplicity of light emitters 5a-5e installed on the ground side, while the optical receiver has an light receiver 6 mounted at a leading end of the vehicle 2. The multiplicity of light emitters 5a-5e are disposed at predetermined intervals along the track 1, as illustrated in FIG. 5, such that they cover a desired vehicle position range R1 in which signal transmission can be achieved.
The multiplicity of light emitters 5a-5e are used in this way because each of the light emitters has a light emitting angle so narrow that a single light emitter cannot cover the desired range R1. In FIG. 5, the position of the vehicle 2 is indicated as the position of the leading end of the vehicle 2 for convenience of explanation. Since the track 1 extends in the horizontal direction in the figure, vehicle positions P0-P2 in the figure are indicated at positions in the horizontal direction in the figure. Position P0 indicates a predetermined stopping position on the platform 3 at which the vehicle 2 should be stopped. The range R1 extends from position P1 to position P2, where position P1 is defined at a position slightly in front of stopping position P0 in the vehicle running direction (indicated by the arrow X) (on the right side in FIG. 5), and position P2 is defined at a predetermined position behind stopping position P0 in the vehicle running direction (on the left side in FIG. 5). Position P2 is set in accordance with the length of the vehicle 2 and a distance over which a continuous safety check is desired for checking whether or not any passenger is caught by a door and dragged after the vehicle 2 has been started from the platform 3.
According to the conventional platform monitoring system, when the vehicle 2 is positioned within the range R1, images representing situations (situations of passengers getting on and off the vehicle) on the platform 3 captured by the cameras 4a-4c are transmitted from the ground side to the side of the vehicle 2 through the light emitters 5a-5e and the light receiver 6, and displayed on the television monitor near the operator""s seat in the vehicle 2. Thus, the operator of the vehicle 2, viewing the display, not only can make a safety check as to whether any passenger is caught by a door while the vehicle 2 remains stopped at position P0 with respect to the platform 3, but also can continue the safety check as to whether any passenger caught by a door is being dragged also in the predetermined range of running immediately after the vehicle 2 has been started.
In addition, according to the conventional platform monitoring system, the optical wireless transmission system is employed as a wireless transmission system for transmitting images from the ground side to the side of the vehicle 2, and light is employed as a transmission medium, so that, unlike the employment of radio waves as a transmission medium, images representing situations on the platform 3 can be transmitted without fail and displayed on the television monitor in the vehicle 2 without suffering from noise which could be generated due to multiple reflection (multipath).
However, since the conventional platform monitoring system requires the multiplicity of light emitters 5a-5e, a higher cost is inevitable, and the installation of the light emitters also requires significant time and labor. Particularly, if a portion of the track 1 behind the platform 3 in the vehicle running direction (on the left side in FIG. 5) is curved, a further increased number of light emitters 5a-5e must be installed, thereby resulting in a further increase in the cost and labor for the installation.
As an alternative, it is contemplated to use a radio wave based wireless transceiver as a wireless transmission system in place of the optical wireless transmission system. In this case, since radio waves tend to be less directive and therefore propagate over a wider range as compared with the light, the number of transmitters can be reduced. It is therefore possible to greatly reduce the cost and labor for installation, as compared with the employment of the optical wireless transmission system.
However, the radio wave based wireless transceiver, if employed, is more susceptible to noise due to multiple reflection (multipath). As a result, depending on a nearby situation (existence of wall surfaces and other buildings), the vehicle 2 may be located at a position at which images available for monitoring for a safety check cannot be displayed on the television monitor at the operator""s seat. Such a position may be coincident with the stopping position P0 of the vehicle 2 with respect to the platform 3. In this event, notwithstanding the fact that the monitoring of situations on the platform 3 is most important when the vehicle 2 remains stopped at the stopping position P0 (i.e., when passengers are getting on and off) for ensuring the safety for the passengers, the monitoring is disabled, which is fatal as the platform monitoring system.
For the reason set forth above, it has been a matter of technical common sense in the field of a platform monitoring system that light should be used, rather than radio waves, as a transmission medium for images representing situations on a platform, and that an increase in the cost and labor for the installation resulting from the employment of the multiplicity of light emitters 5a-5e must be regarded as acceptable.
JP-A-62-16636 discloses an optical space transmission device against a moving body, which is constituted of a plurality of optical transmitters installed on the ground side and an optical receiver installed on a moving body.
JP-A-11-331816 discloses a mobile body optical space transmission system, in which images representing a state on a platform are transmitted to a train by a ground side light transmission device and an on-vehicle side light receiving device.
JP-A-10-304346 discloses an ITV system for confirming safety, in which monitor video images at a station platform by two television cameras are synthesized into one image and the image is transmitted from the station platform to a train by a radio transmitter.
It is an object of the present invention to provide a platform monitoring system which, contrary to the technical common sense as mentioned above, is capable of reliably and appropriately monitoring as required for ensuring the safety for passengers, and is capable of operating with fewer light emitters, thereby reducing the cost and labor for installation thereof.
The results of studies made by the inventors have revealed the characteristics as described below in the platform monitoring system. Specifically, it is most important for ensuring the safety for passengers to monitor situations on a platform when a vehicle remains stopped at a predetermined stopping position with respect to the platform (i.e., when passengers are getting on and off). Therefore, when the vehicle remains stopped at the predetermined stopping position with respect to the platform, images representing situations on the platform must be transmitted to the vehicle side to display the situations without fail. Also, while the vehicle remains stopped at the platform, the operator and so on will be carefully watching images representing situations on the platform, so that the quality of the images are preferably higher. On the other hand, when the situations on the platform are monitored for continuing a safety check as to whether any passenger is caught by a door and dragged in a predetermined range of running immediately after the vehicle has been started from the platform, temporary disturbance on images representing situations on the platform, if any, would not cause any problem for the safety check. In addition, since the vehicle is running, the operator will view the images representing the situations on the platform while paying attentions to the front, i.e., the operator will not watch the images so carefully, the quality of the images may be relatively low for sufficiently accomplishing the purpose.
The present invention has been made by skillfully utilizing the aforementioned characteristics of the platform monitoring system found by the inventors.
Specifically, a platform monitoring system according to one aspect of the present invention comprises an imager device installed on the ground side for capturing a situation on a platform, a wireless transmission unit for transmitting an image captured by the imager device to a vehicle side, and a display unit installed on the vehicle side for displaying an image transmitted by the wireless transmission unit. The wireless transmission unit includes an optical transmitter installed on the ground side for transmitting an image captured by the imager device as an optical signal, a radio wave transmitter installed on the ground side for transmitting the image as a radio wave signal, an optical receiver installed on the vehicle side for receiving an optical signal transmitted from the optical transmitter, a radio wave receiver installed on the vehicle side for receiving a radio wave signal transmitted from the radio wave transmitter, and a selector for selecting one of the optical signal received by the optical receiver and the radio wave signal received by the radio wave receiver. The optical transmitter and the optical receiver are positioned such that a vehicle position range in which signal transmission through the optical signal can be achieved includes a region around a predetermined stopping position of the vehicle with respect to the platform. The radio wave transmitter and the radio wave receiver are positioned such that a vehicle position range in which signal transmission through the radio wave signal can be achieved includes a range from a region around the stopping position to a predetermined position behind the stopping position in a vehicle running direction. Then, an image represented by a signal selected by the selector is selectively displayed on the display unit.
According to this platform monitoring system, as transmission media for transmitting an image representing a situation on a platform captured by the imager device to the vehicle side, both radio waves and light waves are used, such that an image transmitted through one medium is selected by the selector and displayed on the display unit on the vehicle side. Then, the vehicle position range in which signal transmission through the optical signal can be achieved includes the region around the predetermined stopping position of the vehicle with respect to the platform, while the vehicle position range in which signal transmission through the radio wave signal can be achieved includes a range from the region around the predetermined stopping position of the vehicle with respect to the platform to a predetermined position behind the vehicle stopping position in the vehicle running direction.
Therefore, according to the foregoing platform monitoring system, for example, the selector may select an optically transmitted signal when the vehicle remains stopped at the predetermined stopping position, and select an image transmitted through any medium available for signal transmission, selected from the light and the radio waves, when the vehicle is positioned within a vehicle position range which extends from the stopping position to a predetermined position backward from the stopping position in the vehicle running direction. In this way, the situation on the platform can be appropriately monitored in accordance with the characteristics of the platform monitoring system.
Specifically, when the vehicle remains stopped at the predetermined stopping position, an optically transmitted image is displayed on the display unit in the vehicle. Since the optical transmission is free from noise due to multipath, the image representing the situation on the platform is reliably transmitted and displayed on the display unit on the vehicle side without fail.
On the other hand, when the vehicle is positioned within the vehicle position range which extends from the stopping position to the predetermined position backward from the stopping position in the vehicle running direction, an image transmitted through any medium available for signal transmission, selected from the light and the radio waves, is displayed on the display unit on the vehicle side. Therefore, as long as the vehicle is positioned within that range, the image transmitted through radio waves is displayed on the display unit on the vehicle side even if the vehicle is positioned within a range in which the optical transmission is disabled. As previously described, since the radio wave signal transmission is susceptible to noise due to multipath, the vehicle may happen to be at a position (hereinafter referred to as the xe2x80x9ctransmission disabled positionxe2x80x9d) at which images available for monitoring for safety check cannot be displayed on the display unit depending on a nearby situation (existence of wall surfaces and other buildings). However, in the platform monitoring system of the present invention, since the image transmitted through radio waves is displayed on the display unit only when the vehicle lies other than the predetermined stopping position (i.e., while the vehicle is running), the vehicle passes over the transmission disabled position instantaneously so that the image displayed on the display unit merely experiences temporary disturbance. Thus, even within the predetermined range of running immediately after the vehicle has been started from the platform, a safety check can be appropriately continued as to whether or not any passenger is caught by a door and dragged.
Also, in the platform monitoring system, since the vehicle position range in which signal transmission through an optical signal can be achieved is only required to include the region around the predetermined stopping position of the vehicle with respect to the platform, the number of light emitters constituting the optical transmitter can be greatly reduced, thereby making it possible to reduce the cost and labor for the installation as the overall system even in consideration of the requirements for the radio wave transmitter and the radio wave receiver, as compared with the aforementioned conventional platform monitoring system. It should be noted that since radio waves tend to be less directive and therefore propagate over a wider range as compared with the light, the number of radio wave transmitters can be reduced irrespective of whether the track is curved, and little labor is required for installing the radio wave transmitter.
As described above, the platform monitoring system can appropriately perform the monitoring required for ensuring the safety for passengers without fail, and requires fewer light emitters to contribute to a reduction in the cost and labor for the installation.
The selector may be responsive to a transmission state of an optical signal between the optical transmitter and the optical receiver for selecting the optical signal when the optical signal presents a good transmission state, and the radio wave signal when the optical signal does not present the good transmission state. In this implementation, since one of the optical signal and the radio wave signal is selected in accordance with a good or a bad transmission condition of the optical signal, an optically transmitted image is selected when the vehicle remains stopped at the predetermined stopping position, while an image transmitted through any medium available for signal transmission is selected from the optical signal and the radio wave signal when the vehicle is positioned within the vehicle position range which extends from the stopping position to the predetermined position backward from the stopping position in the vehicle running direction.
Alternatively, the selector may include an optical signal level detector for detecting a level of an optical signal received by the optical receiver, wherein the selector may select the optical signal when a level detected by the optical signal level detector is equal to or higher than a predetermined level, and select the radio wave signal when the level detected by the optical signal level detector is lower than the predetermined level. In this implementation, the level of the optical signal received by the optical receiver is used as indicia of a transmission state of the optical signal between the optical transmitter and the optical receiver. Alternatively, data for detecting the transmission state may be added, for example, when an image is encoded, such that a determination as to whether or not the data can be decoded by the optical receiver may be used as indicia of the transmission state of the optical signal between the optical transmitter and the optical receiver.
Further alternatively, the selector may be responsive to the position of the vehicle for selecting the optical signal when the vehicle is positioned in the region around the stopping position, and the radio wave signal when the vehicle is positioned out of the region around the stopping position. Also, in this implementation, an optically transmitted image is selected when the vehicle remains stopped at the predetermined stopping position, while an image transmitted through any medium available for signal transmission is selected from the optical signal and the radio wave signal when the vehicle is positioned within the vehicle position range which extends from the stopping position to the predetermined position backward from the stopping position in the vehicle running direction.
When the position of the vehicle is utilized for the selection in the manner described above, a railway train or the like generally has a detector for detecting its own position, so that a position detection signal from the detector may be used for the selection. Alternatively, another position detector, for example, a GPS position detector or the like may be especially mounted in the vehicle, such that a position detection signal from this position detector may be used.
Further alternatively, the selector may be responsive to a transmission state of an optical signal between the optical transmitter and the optical receiver and a transmission state of a radio wave signal between the radio wave transmitter and the radio wave receiver for selecting (a) the optical signal when the optical signal presents a good transmission state, (b) the radio wave signal when the optical signal does not present the good transmission state and the radio wave signal presents a good transmission state, and (c) a stop of displaying an image represented by the optical signal or the radio wave signal when the optical signal does not present the good transmission state and the radio wave signal does not present the good transmission state. In this event, an image represented by the optical signal or the radio wave signal is not displayed on the display unit when the selector selects the stop of displaying. In this implementation, when the optical signal does not present a good transmission state and the radio wave signal also does not present a good transmission state, an image represented either by the optical signal or by the radio wave signal is not displayed on the display unit. Therefore, even if the platform monitoring system employs a circuit configured to hold and continuously output an image which can be received immediately before the radio wave signal cannot be received, it is possible to avoid a situation in which the most recently received image is continuously displayed although no radio wave signal is being received. In this respect, this implementation is preferable.
Further alternatively, the selector may include an optical signal level detector for detecting a level of an optical signal received by the optical receiver, and a radio wave signal level detector for detecting a level of a radio wave signal received by the radio wave receiver. In this implementation, the selector may select (a) the optical signal when a level detected by the optical signal level detector is equal to or higher than a first level, (b) the radio wave signal when the level detected by the optical signal level detector is lower than the first level and a level detected by the radio wave signal level detector is equal to or higher than a second level, and (c) a stop of displaying an image represented by the optical signal or the radio wave signal when the level detected by the optical signal level detector is lower than the first level and the level detected by the radio wave signal level detector is lower than the second level. In this event, an image represented by the optical signal or the radio wave signal is not displayed on the display unit when the selector selects the stop of displaying. In this implementation, the level of the optical signal received by the optical receiver is used as indicia of a transmission state of the optical signal between the optical transmitter and the optical receiver, while the level of the radio wave signal received by the radio wave receiver is used as indicia of a transmission state of the radio wave signal between the radio wave transmitter and the radio wave receiver. Alternatively, data for detecting the transmission state may be added, for example, when an image is encoded, such that a determination as to whether or not the data can be decoded by the optical receiver or by the radio wave receiver may be used as indicia of the transmission state of these signals.
Further alternatively, the selector may be responsive to a transmission state of an optical signal between the optical transmitter and the optical receiver and a transmission state of a radio wave signal between the radio wave transmitter and the radio wave receiver for selecting (a) the optical signal when the optical signal presents a good transmission state and the radio wave signal presents a good transmission state, (b) the radio wave signal when the optical signal does not present the good transmission state and the radio wave signal presents the good transmission state, and (c) a stop of displaying an image represented by the optical signal or the radio wave signal when the radio wave signal does not represent the good transmission state. In this event, an image represented by the optical signal or the radio wave signal is not displayed on the display unit when the selector selects the stop of displaying.
Further alternatively, the selector may include an optical signal level detector for detecting a level of an optical signal received by the optical receiver, and a radio wave signal level detector for detecting a level of a radio wave signal received by the radio wave receiver. In this implementation, the selector may select (a) the optical signal when a level detected by the optical signal level detector is equal to or higher than a first level and a level detected by the radio wave signal level detector is equal to or higher than a second level, (b) the radio wave signal when the level detected by the optical signal level detector is lower than the first level and the level detected by the radio wave signal level detector is equal to or higher than the second level; and (c) a stop of displaying an image represented by the optical signal or the radio wave signal when the level detected by the radio wave signal level detector is lower than the second level. In this event, an image represented by the optical signal or the radio wave signal is not displayed on the display unit when the selector selects the stop of displaying.
Further alternatively, the selector may be responsive to a position of the vehicle and a transmission state of a radio wave signal between the radio wave transmitter and the radio wave receiver for selecting (a) the optical signal when the vehicle is positioned in the region around the stopping position, (b) the radio wave signal when the vehicle is positioned out of the region around the stopping position and the radio wave signal presents a good transmission state, and (c) a stop of displaying an image represented by the optical signal or the radio wave signal when the vehicle is positioned out of the region around the stopping position and the radio wave signal does not present the good transmission state. In this event, an image represented by the optical signal or the radio wave signal is not displayed on the display unit when the selector selects the stop of displaying.
Further alternatively, the selector may include a radio wave signal level detector for detecting a level of a radio wave signal received by the radio wave receiver. In this implementation, the selector may select (a) the optical signal when the vehicle is positioned in the region around the stopping position, (b) the radio wave signal when the vehicle is positioned out of the region around the stopping position and a level detected by the radio wave signal level detector is equal to or higher than a predetermined level, and (c) a stop of displaying an image represented by the optical signal and the radio wave signal when the vehicle is positioned out of the region around the stopping position and the level detected by the radio wave signal level detector is lower than the predetermined level. In this event, an image represented by the optical signal or the radio wave signal is not displayed on the display unit when the selector selects the stop of displaying.
Further alternatively, the selector may be responsive to the position of the vehicle for selecting (a) the optical signal when the vehicle is positioned in the region around the stopping position, (b) the radio wave signal when the vehicle is positioned out of the region around the stopping position and the vehicle positioned in the range from the region around the stopping position to the predetermined position behind the stopping position in the vehicle running direction, and (c) a stop of displaying an image represented by the optical signal or the radio wave signal when the vehicle is positioned out of the region around the stopping position and the vehicle is positioned out of the range from the region around the stopping position to the predetermined position behind the stopping position in the vehicle running direction. In this event, an image represented by the optical signal or the radio wave signal is not displayed on the display unit when the selector selects the stop of displaying.
An image transmitted through the optical signal may have a quality higher than an image transmitted through the radio wave signal. The optical signal transmission speed is higher than the radio wave signal transmission speed. Therefore, an image transmitted through an optical signal preferably has a higher quality than an image transmitted through the radio wave signal since the image carefully watched by the operator while the vehicle remains stopped at the platform presents a high image quality. It should be noted that the radio wave signal transmission speed is relatively low, so that an image transmitted through a radio wave signal cannot provide a very high quality. Nevertheless, such an image quality serves sufficiently for a safety check. In addition, since the image transmitted through the radio wave signal is displayed on the display unit when the vehicle is found at a position other than the predetermined stopping position (i.e., the vehicle is running), the operator will view the image representing a situation on the platform while paying attention to the front, i.e., the operator will not watch the image so carefully. For this reason, the quality of the image may be relatively low for sufficiently accomplishing the purpose.
Alternatively, the quality of an image transmitted through an optical signal may be identical to the quality of an image transmitted through the radio wave signal. In this implementation, an image encoder circuit for optical transmission and an image encoder circuit for radio wave transmission can be replaced with a single encoder circuit.